Backplane interconnection system is a common circuit board interconnection system. The backplane refers to a component which provides signal coupling, power supply, guidance, and physical support, etc., for one or more functional circuit boards implementing different functions in a communication system such as a switch, a router, a storage device, a computer or a server. Usually, the backplane includes a multi-layer circuit board, signal/power backplane connector, guiding mechanism, etc.
A backplane interconnection system is formed by mounting one or more functional circuit boards implementing various functions on the backplane connectors of the backplane.
FIG. 1 is a mounting structure of an existing backplane interconnection system. As illustrated in FIG. 1, each functional circuit board 12 is parallel to each other and perpendicular to a backplane 10. Each functional circuit board is inserted into a slot on a backplane connector 11 so that the functional circuit board is connected with the backplane 10. The backplane connectors 11 as illustrated in FIG. 1 are on the same side of the backplane 10. In practice, a plurality of backplane connectors 11 may also be located on the two sides of the backplane 10, i.e., the functional circuit boards 12 can be mounted on two sides of the backplane 10.
With the increase of the signal transmission rate, high-speed data buses on the functional circuit boards and the backplane are generally arranged in a point-to-point differential interconnection topology. However, such topology may produce some undesirable effects on the transmission performance of each interconnection path in the backplane interconnection system. For instance, the high-speed data bus for coupling each functional circuit board on the backplane may cause signal attenuation on each interconnection path. Moreover, the length of these high-speed data bus may vary with the space among each backplane connector, causing different extent of signal attenuation on each interconnection path. In addition, FIG. 2 illustrates a schematic of an existing via hole connection section on the backplane in a backplane interconnection system. Multiple via holes 20 connected to the backplane connectors are provided on the backplane. Usually, there exists an unwanted portion 21 with a certain length for the via hole 20. The unwanted portion 21 of the via hole 20 may cause signal reflection.
In addition, the transmission performance of the high-speed backplane interconnection paths may be affected by other factors including material, conductor loss, wiring length, impedance control, delay between two transmission cables of a differential pair, and crosstalk between the differential pair, etc.
For the above reasons, the insertion loss and the return loss on each interconnection path in the backplane interconnection system are different, which increases the difficulty in IC design for the related functional chips on each functional circuit board. Consequently, this hinders the improvement of the transmission rate and the smooth update of the backplane.
In order to overcome the foregoing defects, an orthogonal mounting structure of a backplane interconnection system was proposed. In such structure, multiple functional circuit boards are mounted at two sides of the backplane. Moreover, the functional circuit boards at one side of the backplane are in a plane which is orthogonal to the plane that the functional circuits at the other side are in. FIG. 3 is a mounting structure schematic of an existing orthogonal backplane interconnection system. As illustrated in FIG. 3, a front card 301 and a back card 302 are respectively inserted into the slots on the two backplane connectors which are at two sides of the backplane 300, respectively. The front card 301 at one side of the backplane 300 is in a plane which is orthogonal to the plane that the rear card 302 at the other side is in. The backplane connectors at two sides of the backplane are coupled through via holes on the backplane 300. Thus, a driver or a receiver (chip) on the front card 301 is interconnected with a receiver or a driver (chip) on the rear card 302.
In such mounting structure, the length of signal cables on the circuit board which are used to connect slave circuit boards is shortened. In some case, signal cables can even be eliminated on the backplane. If the pad array in the mounting area for the backplane connector is in diagonal symmetry, that is, the pad array is symmetric along the diagonal of the mounting area for the backplane connector, signal cables can be eliminated. That is, when the pins are on the front card and rear card which are orthogonal to each other, corresponding pins of pins may share a same via hole.
Referring to FIG. 4a˜4c, FIG. 4a is a front view of an existing orthogonal backplane interconnection system. FIG. 4b is a cross-section view of the front card 301 shown in FIG. 4a. FIG. 4c is a right view of an existing orthogonal backplane interconnection system. As illustrated in FIG. 4a˜4c, the signal sent by the driver 311 on the front card 301 is transmitted along a via hole 312 on the front card, differential signal line 313, a via hole 314 to the backplane connector 31 coupled to the front card 301. Then, the signal is further transmitted to a receiver 321 on the rear card 302 along the backplane connector 21, a via hole 30 on the backplane 300, a backplane connector 32 coupled to the rear card 302, a via hole 324 on the rear card, differential signal line 323 and a via hole 322. Each pair of driver and receiver in the orthogonal backplane interconnection system may realize signal transmission in accordance with the approaches shown in FIG. 4a˜4c. 
With regard to the above structure, the existing backplane interconnection system still suffers from the below problems. The inability to control the via impedance may cause severe impedance inconsistency. Moreover, high signal density may result in a considerable crosstalk among via holes, thereby the crosstalk among each interconnection path appears.
Therefore, existing circuit board interconnection system like backplane interconnection system may suffer from a poor transmission performance. Moreover, the transmission rate is slow and the attempt to improve the transmission rate may also be hindered.